Cannabis is a very rapidly growing plant, attaining a usual height of three to twenty feet at maturity. Cannabis is dioecious, which means that there are sexually distinct male and female plants. The known species are Cannabis sativa, Cannabis indica and Cannabis ruderalis with multiple strains in cultivation.
Cannabis use for medicinal purposes dates back at least 3,000 years. It was introduced into Western medicine in the 1840s by W. B. O'Shaughnessy, a surgeon who learned of its medicinal properties while working in India for the British East Indies Company. In most countries, growth and use of Cannabis plants is restricted due to the presence of the psychoactive compound tetrahydrocannabinol (THC), along with a plethora of other cannabinoid compounds, terpenes and phenols that do not necessarily share THC's psychoactive effects. The use of Cannabis is prohibited in many countries as it is considered a drug due to its psychoactive constituent THC.

Some medical uses of Cannabis extracts and isolated compounds are recognized in published peer reviewed literature, as shown in the reference list below, and continue to stimulate increased interest among physicians and patients for multiple medical applications. For instance, cannabis extracts are included in a SATIVEX product approved by regulatory authorities in UK, Spain, New Zealand and Canada to treat spasticity in multiple sclerosis (http://www.gwpharm.com/Sativex.aspx).
U.S. Pat. No. 6,630,507 patent from National Institutes of Health (Hampson et al) describes Cannabis spp. isolated compounds called cannabinoids that have antioxidant La properties, and mentions possible use in the treatment of ischemic, age-related, inflammatory and autoimmune diseases. The cannabinoids are said to have particular applications as neuroprotectants, for example in limiting neurological damage following ischemic insults, such as stroke and trauma, or in the treatment of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease and HIV related dementia. Cannabidiol is mentioned in particular, as it lacks the toxic and psychoactive effects of THC.
